Computer modelling of plastic deformation and fracture in heterogeneous systems.

The results from a computational investigation of plastic deformation and fracture in austenitic steel are presented. A lattice model representing the continuum mechanical behaviour in three-dimensions is developed. The model is shown to recover the governing equations for continuum elasticity theory and is extended to include plasticity through the localised reduction of elastic moduli, and the application of internal forcces in order to maintain stress continuity. The properties of the bonds constituting the lattice are varied in different regions in order to simulate multi-phase materials. The resulting system of equations retains its linearity and is, therefore, solvable using a conjugate gradient algorithm. Fracture is introduced through the iterative removal of bonds, where clusters of bonds normal to a potential fracture plane are considered. The model gives reasonable agreement with theoretical predictions for the elastic fields generated by a spherical inclusion, although for small particle sizes the discretisation of the underlying lattice causes some departures from the predicted values. Results are presented for a spherical inclusion in a plastic matrix and are found to be in good agreement with predictions of Wilner.The deformation and fracture of inclusions due to particles characteristically embedded in austenitic steel are considered. The deformation fields within spherical particles are found to depart from uniformity in the presence of plasticity in the matrix, and their decohesion is in accord with experimental expectations. The model accounts for the internal fracture characteristics of elongated manganese sulphide particles when orientated parallel to the tensile direction. The interaction between two iron carbide particles or two voids are also investigated, and found to be potentially detrimental. Random voidal microstructures are simulated, with subsequent results analysed using Weibull statistical analysis. The maximum stress levels, with respect to the applied stress, are considered and the system size dependence is found to be characteristic of a Weibull distribution. The effects of varying the volume fraction of voids is observed to have a deleterious effect on both the strength and toughness of the simulations

Mathematical Modelling and Computer Simulations in Undergraduate Biology Education

A course in computational biology that introduces undergraduate biology students to mathematical modelling and computer simulations is described. Spreadsheets offer the perfect environment to introduce our biology students to computational thinking and the increasing role that computer simulations are playing in biology research. Here, we detail the spreadsheet modelling of some of the simulations covered in the course; the Lotka-Volterra predator-prey model, a cellular automaton model of tumor growth, and a model of an infectious disease outbreak. The experience of implementing computational biology simulations in a spreadsheet environment encourages and enables our biology students to use computer simulations and spreadsheets more in their future research, and makes our students more comfortable when interpreting scientific literature that pertains to computational biology research. These are important skills that our biology students will need in their future careers as researchers and scientists

Simultaneous optical polarimetry and X-ray data of the near synchronous polar RX J2115-5840

We present simultaneous optical polarimetry and X-ray data of the near synchronous polar RX J2115-5840. We model the polarisation data using the Stokes imaging technique of Potter et al. We find that the data are best modelled using a relatively high binary inclination and a small angle between the magnetic and spin axes. We find that for all spin-orbit beat phases, a significant proportion of the accretion flow is directed onto the lower hemisphere of the white dwarf, producing negative circular polarisation. Only for a small fraction of the beat cycle is a proportion of the flow directed onto the upper hemisphere. However, the accretion flow never occurs near the upper magnetic pole, whatever the orientation of the magnetic poles. This indicates the presence of a non-dipole field with the field strength at the upper pole significantly higher. We find that the brightest parts of the hard X-ray emitting region and the cyclotron region are closely coincident.Comment: 9 pages, accepted for publication in MNRAS 2 March 200

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy

Centrality dependence of inclusive J/ψ production in p-Pb collisions at s N N = 5.02 sNN=5.02 \sqrt{s_{\mathrm{NN}}}=5.02 TeV

We present a measurement of inclusive J/psi production in p-Pb collisions at root S-NN = 5.02 TeV as a function of the centrality of the collision, as estimated from the energy deposited in the Zero Degree Calorimeters. The measurement is performed with the ALICE detector down to zero transverse momentum, p(T), in the backward (-4.46 < y(cms) < -2.96) and forward (2.03 < y(cms) < 3.53) rapidity intervals in the dimuon decay channel and in the mid-rapidity region (-1.37 < y(cms) < 0.43) in the dielectron decay channel. The backward and forward rapidity intervals correspond to the Pb-going and p-going direction, respectively. The p(T)-differential J/psi production cross section at backward and forward rapidity is measured for several centrality classes, together with the corresponding average p(T) and p(T)(2) values. The nuclear modification factor is presented as a function of centrality for the three rapidity intervals, and as a function of p(T) for several centrality classes at backward and forward rapidity. At mid-and forward rapidity, the J/psi yield is suppressed up to 40% compared to that in pp interactions scaled by the number of binary collisions. The degree of suppression increases towards central p-Pb collisions at forward rapidity, and with decreasing p(T) of the J/psi. At backward rapidity, the nuclear modification factor is compatible with unity within the total uncertainties, with an increasing trend from peripheral to central p-Pb collisions

Simulating the co-encapsulation of drugs in a “smart” core-shell-shell polymer nanoparticle

A coarse-grained lattice Monte Carlo method is used to simulate co-encapsulation and delivery of both a hydrophilic and hydrophobic drug from polymer nanoparticles. In particular, core-shell-shell polymer nanoparticles with acid-labile bonds are simulated, and the preferential release of the encapsulated drugs near more acidic tumors is captured. While these simple models lack the molecular details of a real system, they can reveal interesting insights concerning the effects of entropy and enthalpy in these systems